Conventionally, there have existed form-fill-seal machines for producing bags by shaping a sheet of a packaging material into a tube and, in a state where the interior thereof has been filled with a snack food or other packaged article, laterally sealing the upper and lower end parts of the packaging material. For example, an upright form-fill-seal machine uses a shaping member or the like to shape a sheet of a packaging material into a tube, and then vertically seals both vertically overlapping edges of the tubular packaging material. During a state where a dropped packaged article is located in the interior space of the tubular packaging material, the upper and lower end parts of a portion of the tubular packaging material serving as a single bag are laterally sealed in sequence, forming a lower sealed part and an upper sealed part in a state where the packaged article is present within the tubular packaging material. To be specific, a lateral seal is made across the leading portion of the bag serving as the upper end part and the following portion of the bag serving as the lower end part, and immediately thereafter (or, alternatively, at the same time) the middle of the lateral seal portion is vertically separated by a cutter, thus forming the tubular bag material into a lower sealed part and an upper sealed part. By repeating such an operation, a form-fill-seal machine continuously produces bags filled with packaged articles.
In a case where potato chips or other articles having a low specific gravity are the packaged article with which the bag is filled, articles in a group may undergo greater vertical separation as they fall, and get caught in the lateral seal portions. Various companies have been devoted to innovations for preventing poor sealing caused by this “catching” phenomenon, such as the technology disclosed in Japanese Laid-Open Patent Application No. 2002-59905.